There are currently few quantitative methods for in vivo measurements of lung water accumulation. The most readily applied methods involve the use of multiple indicator dilution studies with diffusible and non-diffusible tracers. These methods have not been applied extensively because of the inability to discriminate between altered states of pulmonary perfusion and real changes in lung water. This proposal is directed toward discriminating pulmonary vascular recruitment from pulmonary edema. The proposal is based on the use of a lipid soluble tracer as a tissue perfusion marker. The studies proposed are a systematic investigation of factors influencing recruitment and water accumulation in animal models, human volunteers, and patients in respiratory failure.